Re: [Qemu-devel] [PATCH RFC for-2.6 1/3] HBitmap: Introduce "meta" bitmap to track bit changes

[Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com>]

On 07.12.2015 08:59, Fam Zheng wrote:
> The meta bitmap will have the same size and granularity as the tracked
> bitmap, and upon each bit toggle, the corresponding bit in the meta
> bitmap, at an identical position, will be set.
>
> Signed-off-by: Fam Zheng <famz@redhat.com>
> ---
>   include/qemu/hbitmap.h |  7 +++++++
>   util/hbitmap.c         | 22 ++++++++++++++++++++++
>   2 files changed, 29 insertions(+)
>
> diff --git a/include/qemu/hbitmap.h b/include/qemu/hbitmap.h
> index bb94a00..09a6b06 100644
> --- a/include/qemu/hbitmap.h
> +++ b/include/qemu/hbitmap.h
> @@ -181,6 +181,13 @@ void hbitmap_iter_init(HBitmapIter *hbi, const HBitmap *hb, uint64_t first);
>    */
>   unsigned long hbitmap_iter_skip_words(HBitmapIter *hbi);
>   
> +/* hbitmap_create_meta
> + * @hb: The HBitmap to operate on.
> + *
> + * Create a "meta" hbitmap to track dirtiness of the bits in this HBitmap.
> + */
> +HBitmap *hbitmap_create_meta(HBitmap *hb);
> +
>   /**
>    * hbitmap_iter_next:
>    * @hbi: HBitmapIter to operate on.
> diff --git a/util/hbitmap.c b/util/hbitmap.c
> index 50b888f..3ad406e 100644
> --- a/util/hbitmap.c
> +++ b/util/hbitmap.c
> @@ -81,6 +81,9 @@ struct HBitmap {
>        */
>       int granularity;
>   
> +    /* A meta dirty bitmap to track the dirtiness of bits in this HBitmap. */
> +    HBitmap *meta;
> +
>       /* A number of progressively less coarse bitmaps (i.e. level 0 is the
>        * coarsest).  Each bit in level N represents a word in level N+1 that
>        * has a set bit, except the last level where each bit represents the
> @@ -232,6 +235,7 @@ static inline bool hb_set_elem(unsigned long *elem, uint64_t start, uint64_t las
>   /* The recursive workhorse (the depth is limited to HBITMAP_LEVELS)... */
>   static void hb_set_between(HBitmap *hb, int level, uint64_t start, uint64_t last)
>   {
> +    uint64_t save_start = start;
>       size_t pos = start >> BITS_PER_LEVEL;
>       size_t lastpos = last >> BITS_PER_LEVEL;
>       bool changed = false;
> @@ -252,6 +256,9 @@ static void hb_set_between(HBitmap *hb, int level, uint64_t start, uint64_t last
>           }
>       }
>       changed |= hb_set_elem(&hb->levels[level][i], start, last);
> +    if (hb->meta && level == HBITMAP_LEVELS - 1 && changed) {
> +        hbitmap_set(hb->meta, save_start, last - save_start + 1);
> +    }

I thing now, that the same may be accomplished for BdrvDirtyBitmap, all 
we need is return "changed" status from hb_set_between and then from 
hbitmap_set.

>   
>       /* If there was any change in this layer, we may have to update
>        * the one above.
> @@ -298,6 +305,7 @@ static inline bool hb_reset_elem(unsigned long *elem, uint64_t start, uint64_t l
>   /* The recursive workhorse (the depth is limited to HBITMAP_LEVELS)... */
>   static void hb_reset_between(HBitmap *hb, int level, uint64_t start, uint64_t last)
>   {
> +    uint64_t save_start = start;
>       size_t pos = start >> BITS_PER_LEVEL;
>       size_t lastpos = last >> BITS_PER_LEVEL;
>       bool changed = false;
> @@ -336,6 +344,10 @@ static void hb_reset_between(HBitmap *hb, int level, uint64_t start, uint64_t la
>           lastpos--;
>       }
>   
> +    if (hb->meta && level == HBITMAP_LEVELS - 1 && changed) {
> +        hbitmap_set(hb->meta, save_start, last - save_start + 1);
> +    }
> +
>       if (level > 0 && changed) {
>           hb_reset_between(hb, level - 1, pos, lastpos);
>       }
> @@ -384,6 +396,9 @@ void hbitmap_free(HBitmap *hb)
>       for (i = HBITMAP_LEVELS; i-- > 0; ) {
>           g_free(hb->levels[i]);
>       }
> +    if (hb->meta) {
> +        hbitmap_free(hb->meta);
> +    }
>       g_free(hb);
>   }
>   
> @@ -493,3 +508,10 @@ bool hbitmap_merge(HBitmap *a, const HBitmap *b)
>   
>       return true;
>   }
> +
> +HBitmap *hbitmap_create_meta(HBitmap *hb)
> +{
> +    assert(!hb->meta);
> +    hb->meta = hbitmap_alloc(hb->size, hb->granularity);
> +    return hb->meta;
> +}


-- 
Best regards,
Vladimir
* now, @virtuozzo.com instead of @parallels.com. Sorry for this inconvenience.